Detergent compositions such as hair shampoos, hand cleansing liquids, bath foam and shower gels typically comprise one or more surfactants to provide cleaning. Such detergent compositions are often thickened to impart the desired rheology for their particular applications. A structurant may be used (either internal or external). This can impart higher levels of storage stability to the composition and it may provide it with enough structure to be able to suspend included solids or gasses, such as perfume capsules or air bubbles.
Structuring may be provided by using a higher level of surfactant than is needed for cleaning. Such surfactant containing detergent compositions, especially compositions comprising mixed surfactants, tend to be highly thixotropic, or even to gel, and this can provide the desired thickening and/or structuring. By higher levels, we mean 7 to 25 percent total surfactant when 2 to 3 percent would suffice for cleaning duty.
Many biopolymers can form reversible gels in aqueous solution. Polysaccharides, which form reversible gels and may be used as rheological additives include agar, carrageenan, furcellaran, gellan and pectin. However, though technically useful these biopolymers are more expensive than surfactants, so there is no incentive to remove surfactant and to use these materials instead. The more effective structurants may also suffer from being derived from materials, or are made using processes, that make them potentially undesirable for inclusion in a product that contacts skin and may get into the eyes.
Cellulose is a plentiful, and consequently inexpensive, biopolymer. However, in its unmodified form it is completely insoluble and cannot be dispersed into an aqueous liquid composition to achieve a stable, thickened, product.
The prior art discloses modified celluloses and their use in detergent compositions.
Complete oxidation of cellulose makes it soluble, as described in GB 1299646 and GB 1330123. Formation of polycarboxylic acids from cellulose sources is taught to be desirable in order to transform the cellulose into a detergency builder. Such modified cellulose builders require intensive processing to oxidise them sufficiently. This makes them more expensive than typical surfactants. In addition, highly oxidised cellulose tends to depolymerise and this leads to loss of structuring capability when the modified cellulose is used in aqueous systems.
In U.S. Pat. No. 5,437,810 liquid detergent compositions are viscosity modified using oxidised polysaccharide with an acid index value of 1 to 20. In its fully oxidised form, cellulose may be converted to polyglucuronic acid, which, because of its high solubility, is unsuitable as a structurant.
GB 709941 describes a process for the production of undecomposed cellulose oxidation products and the use of such products and their salts in detergent formulations. Cellulose based woody raw materials are selectively oxidised at the primary alcohol (C6) position on the anhydroglucose units. This process appears to oxidise the cellulose as much as possible. It also teaches to use low levels of the material when surfactant is present. The benefit is said to be improved detergency, presumably due to the builder effect of the oxidised cellulose. Builder materials are also taught in U.S. Pat. No. 4,056,400.
Like C6 oxidised cellulose, pectin has C6 acid groups. However, it differs from C6 partially oxidised cellulose because instead of residual primary alcohol groups it has methylated acid groups. This that makes it soluble and it therefore behaves differently in the presence of anionic or amphoteric surfactants.
Chitin can be modified to make anionic polymers by partially oxidising the primary alcohols as taught in U.S. Pat. No. 6,037,460, especially examples 7, 8, 9 and 11 where it is used to thicken a detergent composition. These chitin derivatives are very expensive and do not exhibit good structuring properties with a wide range of surfactants.
Partially and selectively oxidising cellulose at the C6 position creates cellouronates or cellouronic acids which are more water dispersible than cellulose but still relatively insoluble. Similar modified celluloses have been used in wound dressings, but for that purpose, the targeting of oxidation onto the C6 primary alcohols has not been important. C6 acids are made in the well known carboxymethyl cellulose, but this has an additional CH2 separating the acid group and the C6 carbon. Because of this, and its high degree of oxidation, CMC is soluble.
Two recent patent publications refer to C6 oxidised modified cellulose material. JP2006 241601 relates to pulp modification for paper making. Oxidation of the C6 groups to aldehydes is said to give greater wet strength to the paper. In JP2008 001728, the same inventor oxidises a variety of cellulose starting materials using the same catalytic route and then by using very high shear dispersions obtains a gel of oxidised cellulose nanofiber. No surfactant is used or added to the dispersion.
The formulator would like to have an alternative structurant for aqueous detergent compositions that is safe to use, is cheaper than the surfactant it replaces, and that can be used with a range of surfactants to allow the level of surfactant to be lowered to that required for the cleaning duty, whilst maintaining the ability to provide detergent compositions of the required rheological profile and clarity.